Apparatus for aiding high altitude ignition in jet power plants



June 19, 1951 J. CROSS ETAL APPARATUS FOR AIDING HIGH ALTITUDE IGNITIONIN JET POWER PLANTS Filed Jan. 13, 1950 Time- INVENTORS James M Cross 1BY Norman E W/rifc/wrcfi ATTORNEY Patented June 19, 1.951

APPARATUS FOR AIDIN G HIGH ALTITUDE IGNITION IN JET POWER PLANTS JamesW. Cross, Kent, and Norman E. Whitchurch, Akron, Ohio, assignors toGoodyear Aircraft Corporation tion' of Delaware Akron, Ohio, a corpora-Application January 13, 1950, Serial No. 138,304 4 Claims. (01. 315-441)This invention relates to an electric ignition apparatus and inparticular to an apparatus for aiding high altitude burning and.ignition in jet power plants.

The advent of the jet power plant has necessitated a re-evaluation ofthe problem of igniting fuel-air mixtures. The low energy electric sparkignition systems used on reciprocating engines have been found to beunsatisfactory, particular,-v ly when used on jet power plants at highaltitude. Tests have shown that at reduced pressures, a high energyspark is required. to ignite the fuelair mixtures. Under startingconditions the combustion chamber pressure in a jet power plantdecreases with increasing altitude. Therefore, at, the reduced pressuresencounteredat high altitudes, a low energy spark will not provide goodignition. One type of jet engine ignition system present.- ly 'in useconsists of a high voltage transformer which fires one spark plug. Onedisadvantage of this system is a result of the reduced breakdown voltageof a sparkgap at reduced pressure. .Because of this reduced breakdownvoltage, the peak energy in the spark'is reduced as the altitude isincreased; consequently, thissystem is inadequate for high-altitudeignition.

Another type of system now inuse has a lowvoltage, high-energy ignitionspark which is initiated by a high-voltage, low-energy trigger spark.This system does not make the most efficient use of the spark energy.Tests have shown that a high peak energy spark produces better ignitionthan a low peak energy spark of equal total energy. This high peakenergy can best be supplied by a high voltage discharge. The systemaccording to this invention provides just such a high-energy,high-voltage spark. In addition, it anticipates the possible future needfor several spark sources to be positioned as desired in the combustionzone by firing any required number of spark plugs.

It is the general object of this invention to avoid and overcome theforegoing and other difl'lculties of and objections to prior artpractices by theprovision for jet power engines of a triggered multipleignition system which produces high peak energy sparks which positivelyignite fuel-air mixtures at the low pressures occurring at highaltitudes.

Another object of the invention is to control the firing of the enginespark plugs by an enclosed spark gap switch of high breakdown voltage.

, Another obj ct of the invention is to provide a high energy ignitionsystem requiring no movable parts.

The aforesaid objects and other objects which will become apparent asthe description proceeds are achieved by providing an ignition systemwhich essentially consists of a high-voltage power. source furnishingdirect current for the ignition circuit to which are connected inparallel one or more energy storage capacitors, each of which isconnected in series with a spark plug, and of a fast acting low-lossswitch connected across the ignition circuit which prevents thecapacitors from discharging through the plugs until the desired amountof energy at proper voltage has been stored. These capacitors may becharged in various ways, described later on, and from any suitablesource of high D. C. voltage which, according to the followingdescription, is obtained by half-wave rectification of a high voltage.

source. In the following circuits a self-triggering, enclosed spark gaphas been used as the switch, but other suitable fast acting, low-lossswitches, e. g., a hydrogen thyratron, and external triggering may beused if desired.

For a better understanding of the invention, reference should now be hadto the accompanying drawing, wherein:

Fig. 1 illustrates a basic circuit of the system, according to theinvention.

Fig. 2 shows a voltage-time diagram of the circuit of Fig. 1. v

Fig. 3 shows an improved modification of the ignition system shown inFig. 1.

Fig. 4 shows a voltage-time diagram of the circuit of Fig. 3.

With specific reference to the form of the invention illustrated in Fig.1 of the drawing, the numeral l indicates an alternating current source,provided with a main switch 2 for closignition ing the current into thehigh voltage transformer 3 from where it passes through a rectifier 4 asdirect current which flows in the main circuit 5, 6 to charge a chargingcapacitor 1 connected across the circuit 5, 6. The charging capacitor 10per-' ates upon storage capacitors 8a., 8b 8n, each connected in serieswith ignitor gaps, or spark plugs 9a, 9b .Bn, respectively, and upon aself-triggering, enclosed spark gap or switch l0 requiring a much highervoltage for firing.

The operation of the system is as follows:

Upon closing the main switch 2, the alternating voltage source I isapplied to the transformer 3."

Charging capacitor 1 charges through the rectifier 4 to a voltage largeenough to fire one of the ignitor gaps, say 9a. Thisallows chargingca-.

pacitor l to discharge into storage capacitor 8a and the discharge willcease when the voltage on charging capacitor 1 is approximately equal tothe voltage on storage capacitor 8a. When the discharge across capacitori ceases capacitor 1 will recharge, but, because of the opposing voltagestored in capacitor 8a during the previous discharge, ignitor gap 80',will not fire again until each of the other ignitor gaps has fired inturn. After all of the ignitor gaps have fired, charging. capacitor 1must charge to a higher voltage before the ignitor gaps will fire againbecause of the charges left in the storage capacitors.- Thus the ignitorgaps will continue to fire and the voltage on the charging capacitor 7will rise in steps to a voltage high enough to eventually fire theswitch gap In. The charging process is nowcomplete,

and upon firing of gap Hi all of the energy storage capacitors willdischarge simultaneously through their associated ignitor gaps and thetrigger or switch gap i0. This-discharge will provide high energy sparksas contrastedwith the previous low energy charging sparks. This process,which repeats itself, is diagrammatically illustrated-in- Fig. 2 inwhich the voltages across the charging capacitor and across the storagecapacitors are indicated against time. It clearly shows how the voltageacross the storage capacitors rises in steps until the voltage across 1reaches the breakdown voltage of the switch gap and the firing of whichsimultaneously fires all spark gaps at high energy.

For example, if it be assumed. that the D. C. supply voltage is 14,000volts, that the spark plugs are set-to fire atabout 5560 volts and thegap switch at 10,009 volts, and that the charging and storage capacitorsare identical, then the charging capacitor .7 will charge up to about5500' volts and fire the spark plugs 9a, 9b 9n, oneaafter another. Then,because of the opposing voltage left onthe storage capacitors 8a, 8b 8n,the charging capacitor will charge to about 8250 volts-before the sparkplugs fire again. However, duringthe next'step the storage capacitor!will' reach a voltage of 10,000 volts, at which voltage the spark gapswitch in and all spark plugs will fire at one and the same time at highenergy.

The energy represented by this discharge is a function of the capacityof the energy storage capacitors, the breakdown voltage of the triggergap, and the breakdown voltage of the'ignitor gaps. The voltage'at whichthe high energy discharge takes place can be shown to be approximatelyequal to the breakdown Voltage of the trigger gap minus the breakdownvoltage of a single ignitor gap. Thus, decreasing the breakdown voltage"of the ignitor gap results in increasing energy in the discharge. Forthis reason the above system is particularly applicable to'jet aircraftengines. Under starting conditions, at high altitudes, the greatlyreduced combustion chamber-pressure results in a lower breakdownvoltage; This isaccompanied by an increase in park energy. which isdesirable for improved ignition at high altitudes.

Since-the breakdown of the trigger gap results in rapid discharge ofenergy across the ignitor gaps, any carbon deposit which would normallyresult in' fouling 'of the-gaps will be burned. away by the high:temperature of the spark. This will result in longer, more reliableignitor operation. Similarly, becauseof the nature-of the system, asingle damaged plug will not result ina failureof the balance ofthe'system. Thi'ssys tem is relatively insensitive to fluctuations involtage. Lowering the supply voltage results in a lowered sparkrepetition rate, but does not change the energy per spark. The systemoperation is not afiected by the use of long cables to the ignitor-gapsor spark plugs, since a relatively high capacity and a relatively'lowshunt resistance across the ignitor gaps can be tolerated.

The most important features of the system can be summarized asfollows:

1;. Energy increases with increasing altitude.

2. Fires any number of plugs.

3. Will fire fouled plugs.

4. A damaged plug does not materially affect the operation. of otherplugs.

5. No moving parts.

6. Canbe madeinsensitive to large supply voltage fluctuations.

'7. Highvoltage spark makes the most eflicient use of spark energy.

8 Unaffected bylong ignition cables.

By a slight modification of the circuit of-Figpl, as shown'Fig. 3, asystem with somewhat different characteristics can be obtained,

It is-apparen-t that this circuit has been obtained from the circuit ofFig. 1 by removing the charging capacitor 'l and inserting asuitableresistance in: the .main circuit branch 5, G leading from therectifier 4-, and resistances [2a, l2b I212; inv parallel with eachspark plug. The operation of the circuit is the same as that' of thefirst circuit, with the important exception that the energystorage-capacitors 9a, 9b 912 now charge'throu'ghthe resistancesshunting the plugs instead of through the plugs as before.(3onsequently, the breakdown voltage ofthe plugs no longer influencesthe voltage built up on the capacitors. The energy per spark is,therefore, constant and independent' of altitude. It is cletermined onlyby the size of the capacitors; the peak: D. 0. supply voltage, thebreakdown-voltage of the gap H1, and the ratio ofthe plug shuntresistorsto the charging resistor H. In addition, since" the capacitorsare charged directly from the source of D.-C;-voltage,- the efficiencyof the circuitlissomewhat-higher than that of Fig. 1 It is interestingto note that the plugshunt re'-' sistances: I 2a-,..l2b We may bereduced to resistance values well below ohms without afiecting'thafiringof the plug. This is anin dication of the: ability of the-system to firefouled plugs.

The most important features of the system are the same asthose of theprevious system, except that. the: energy per spark is constantand in'-'dependent of altitude, andthe eflici'ency i -greater.

In the voltage -timediagram, Fig. 4, it is seen thatthe storage:capacitors are allcharged sim ultaneously to. a; voltage nearly equaltothat necessary tob'reakzdownz the enclosedztrigger gap 16,. whichthereby causes to fireall spark plugs by discharging allstorage;capacitors simultaneously, and to-thereby obtain'high energy-sparkswhich. will positively ignite fuel-air mixtures in starting ajet engineat high altitude.

From the aforesaid it will be recognized that the objects of theinvention have been fully achieved; and that with this system'ofrelatively low weight'without any moving parts, high spark.

energy at high voltage can be producedto. posi-. tively igniteair-fuelmixtures at high altitudes forstarti'ng a .jet" engine.

While certain representative embodiments and details'have beenshownforthe purpose of illus- 7'5 tratingtheinvention, it will beapparent to those skilled in the art that various changes andmodifications may be made therein without departing from the spirit orscope of the invention.

What we claim:

1. A high voltage discharge apparatus for jet aircraft ignition or thelike including a high direct current voltage source, a plurality ofspark plugs, a storage condenser in series with each plug, means forcharging said condensers from the direct current voltage source, and aself-triggered switch in parallel with the spark plugs and associatedcharging condenser.

2. A high voltage discharge apparatus for jet aircraft ignition or thelike including a high direct current voltage source, a plurality ofspark plugs, a storage condenser in series with each plug, means forcharging said condensers from the direct current voltage source, and anenclosed self-triggered spark gap switch having a breakdown voltagehigher than that of the spark plugs in parallel with the spark plugs andassociated charging condenser.

3. Apparatus comprising an electric ignition circuit for turbo jet andram jet engines in an aircraft operating at high altitudes, a highvoltage direct current source supplying said circuit, a chargingcapacitor connected in parallel with said circuit, at least one energystorage capacitor connected in parallel with said charging capacitor, aspark plug connected in series with each of said storage capacitors, andan enclosed selftriggering spark gap switch of predetermined butsubstantially higher breakdown voltage than that of the spark plugs andconnected across said circuit, said charging capacitor being charged toa voltage substantially equal to that of the breakdown voltage of thespark plugs for firing one spark plug, whereby the charging capacitorcharges the corresponding storage capacitor until the voltage of thecharging capacitor about equals that of the storage capacitor, thisspark plug, because of the opposing voltage of its storage capacitorwill not fire again until each of the plugs has fired in turn, after allof the spark plugs have fired the charging capacitor must charge to ahigher voltage before the spark plugs will fire again because of thecharges left in the storage capacitors, thus, the gaps will continue tofire and the voltage on the charging capacitor will eventually fire saidspark gap switch, the charging process is now complete and upon firingof said gap switch all of the energy storage capacitors will dischargesimultaneously through their associated spark plugs and said switch gapproviding high energy sparks in contrast to the previous low energycharging sparks.

4. Apparatus comprising an electric ignition circuit for turbo jet andram jet engines in an aircraft operating at high altitudes, a highvoltage direct current source supplying said circuit, a chargingresistor in said circuit, at least one energy storage capacitorconnected in parallel therewith, a spark plug connected in series witheach of said storage capacitors, a shunting resistor in parallel witheach spark plug for simultaneously charging all storage capacitorsthrough said shunting resistors, and an enclosed spark gap switch ofpredetermined high breakdown voltage substantially higher than that ofsaid spark plugs and connected across said circuit being adapted to firesimultaneously and periodically all spark plugs at high energy.

JAMES W. CROSS. NORMAN E. WHITCHURCH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,040,439 Langer May 12, 19362,125,035 Smits July 26, 1938 2,297,006 Lohman Sept. 29, 1942

